Priority is claimed on Japanese Patent Application No. 2007-28312, filed Feb. 7, 2007, and Japanese Patent Application No. 2007-29114, filed Feb. 8, 2007, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a seatbelt device for restraining an occupant who is seated in a seat of a vehicle using a webbing, and more particularly, to a seatbelt device of a vehicle having a pretensioner mechanism using a motor.
2. Description of Related Art
A conventional seatbelt device that changes tension of the seatbelt in accordance with a driving state of a vehicle (e.g., see Japanese Unexamined Patent Application, First Publication No. 2004-291967) has been known.
In recent years, as such a seatbelt device, there has been proposed a practical seatbelt device which includes a motor for driving a belt reel to rotate and which controls tension of a webbing by driving the motor, in an emergency state or an unstable driving state so as to stabilize the posture of an occupant (e.g., see Japanese Unexamined Patent Application, First Publication No. H06-286581).
The seatbelt device includes a pretensioner mechanism for pulling the webbing using a motor upon detecting a warning sign of a collision in addition to an emergency restraining unit for abruptly pulling the webbing using a large force that is generated by the explosive power of gunpowder when a large shock is input to a vehicle due to a collision and the like.
The conventional seatbelt device operates the pretensioner mechanism upon detecting a warning sign of the collision. However, comparatively large restraint force is necessary since the restraint force of the webbing has to maintain the posture of the occupant. For this reason, when a threshold value (e.g., a threshold deceleration value of a vehicle) at which the pretensioner mechanism starts to operate is set to a small value, it is uncomfortable for the occupant in that the pretensioner mechanism frequently and strongly restrains the occupant.
Accordingly, in the conventional seatbelt device, the threshold value at which the pretensioner mechanism starts to operate is set to a comparatively large value so that the pretensioner mechanism does not operate too frequently.
Currently, there has been a demand for a seatbelt device capable of pulling the webbing to stabilize the posture of the occupant who drives the vehicle not only upon detecting the warning sign of the collision, but also upon turning the vehicle or operating VSA (Vehicle Stability Assist: vehicle movement stabilization control system).
In the conventional seatbelt device, if only the tension of the seatbelt changes in accordance with the driving state of the vehicle, the restraint force for performing a protection restraint and for suppressing variation in the posture of the occupant may become considerably large. As a result, a problem arises in that it may cause unacceptable discomfort to the occupant.
Additionally, since a tension sensor for detecting the tension of the seatbelt needs to be provided additionally, the configuration of the apparatus becomes complex. Also, in a case where the seatbelt is controlled to be in a predetermined tension state, it is necessary to use a sufficient tension so as to be able to handle abrupt changes in the driving state of the vehicle. Additionally, since it is difficult to restrain the occupant in a desired state using relatively small tension, a problem arises in that it causes unacceptable discomfort when suppressing a variation in the posture of the occupant. In particular, when an abrupt variation in tension occurs due to a variation in the posture of the occupant, if the seatbelt is controlled to maintain a target tension state, a problem arises in that excessive tension occurs, causing unacceptable discomfort to the occupant, or, in the contrary, the seatbelt is loosened.